1. Field Of The Invention
The present invention relates generally to cement plug containers, and more particularly, but not by way of limitation, to a lift through cement plug container for use with a slant drilling rig.
2. Description Of The Prior Art
It is common in the drilling of wells to utilize various forms of directional drilling to control the path of a bore hole as it is drilled into the earth.
One technique which has been developed is the use of a slanted drilling rig having a tilted mast, so that the bore hole actually enters the earth's surface at an angle determined by the angle of tilt of the mast. Such a slant drilling rig is described, for example, in Oil & Gas Journal, May 14, 1984, pages 72-74, in the article entitled "Slant Holes Tap Shallow Gas Under Lake".
These slant rigs include a tilted mast having a pair of spaced rails with an elevator spanning between the rails. The elevator moves along a length of the rails for reciprocating a drill string or casing string supported thereby. The mast is open on its generally upward facing side to provide access to the pipe string supported from the elevator.
Various types of plug containers are also known to the art. For example, the assignee of the present invention markets through its Halliburton Services Division a Jet-Hed.TM. III plug container such as that shown in Halliburton Services Sales & Service Catalog No. 43 at page 2423 (1985). A similar plug container having modified fluid inlets is shown in U.S. Pat. No. 4,290,482 to Brisco, and also assigned to the assignee of the present invention. Cement plug containers like those just cited are not "lift through" designs in that they are not designed to support the weight of the casing string through the structure of the plug container. Instead, the casing string must be supported at some point below the plug container.
Also known to the art are cementing heads of the "lift through" design wherein the entire weight of the drill pipe which is hung below the drilling platform is supported through or lifted through the structure of the cementing head. One such system is that known as the Nodeco system which is shown in Exhibit A filed herewith. The Nodeco system utilizes a lifting sub attached to the upper end of a container body. The container body does not hold a cement plug. Instead, it contains balls and darts which are dropped to a subsurface plug container wherein the actual cementing plugs are activated by the balls and darts.
In all of the cement plug container or cementing head designs cited above, the cement line manifolds and plunger assemblies are typically arranged so that they span at least 180.degree. about the axis of the container, and in many cases projections from the container protrude in all quadrants about the container. Accordingly, these typical prior art containers are problematic when utilized with a slant rig like that discussed above wherein the pipe string and any associated apparatus such as a cement plug container must be suspended from the elevator between the rails of the tilted mast.
There is a need for a cement plug container particularly adapted for use with slant rigs.